1. Field of the Invention
The present invention relates to an improved method of preparing a grease, and to the grease produced thereby.
2. Description of Related Arts
The use of grease to lubricate fittings is well known to persons skilled in the art. Grease is essentially thickened oil, and because of its viscosity is well suited for lubricating surfaces where oil might run off or drip.
Polychlorotrifluoroethylene polymer of controlled molecular weight has been used by the assignee of this application as a thickening agent, which is then incorporated into polychlorotrifluoroethylene oil for the preparation of a grease. The grease produced is characterized by excellent properties.
In the process of making this grease, the molecular weight of the polymer must be carefully controlled in order to achieve acceptable results, and for this purpose use had been made previously of carbon tetrachloride as a telogen.
However, carbon tetrachloride, because it is harmful to the ozone layer and the environment, is no longer a desirable telogen. Therefore, a search was made to find a suitable substitute for carbon tetrachloride.
From other work in the telomerization field, one would expect that chloroform could be used as a substitute for carbon tetrachloride. It is well known that chloroform in large ratios to chlorotrifluoroethylene [R-1113] was used to make chlorotrifluoroethylene oils of the type used here. See, for example, Preparation, Properties, and Technology of Fluorine and Organic Fluoro Compounds, edited by Charles Slesser and Stuart R. Schram, McGraw-Hill Book Company, Inc., 1951, page 607. However, the results that we have achieved using chloroform to make higher controlled molecular weight polymers have been disappointing.
The use of 2,2-dichloro-1,1,1-trifluoroethane [R-123] as polymerization medium in the preparation of fluorine polymers having fluoroolefin units as building blocks is known from Japanese Unexamined Patent Publication No. 6-340718, which was laid open on Dec. 13, 1994. R-1113 is listed as an example of a fluoroolefin monomer useful in the process disclosed therein. However, there is no mention therein of its use as a thickening agent for incorporation into polychlorotrifluoroethylene oil for the preparation of a grease.
Moreover, the Japanese application actually teaches away from the use of R-123 as a telogen. The Japanese application teaches that R-123 provides "some" chain transferring. However, the Japanese application expressly teaches that chain transfer compounds usually must be added to the reaction medium to control the molecular weight of the polymer. Therefore, the use of R-123 as an acceptable telogen per se cannot be gleaned from the Japanese application. The clear suggestion is that telogen additives must be employed; the R-123 alone is insufficient.
Further, the examples of the Japanese application lead to the use of very high amounts of R-123 as solvent. The amounts of R-123 employed are approximately 2.5 and 10 times the amount of monomers employed.
U.S. Pat. No. 5,182,342 describes a process for the free radical polymerization of fluoromonomers, including R-1113, in selected hydrofluorocarbon solvents. The teachings of the patent purport to be very broad, and appear to embrace also the use of R-123 as the polymerization solvent. However, R-123 is not specifically mentioned as an example. Moreover, there is no teaching therein that R-123 is an acceptable telogen per se, nor is there any teaching therein of the use of the resulting polymer in the preparation of a grease.
Accordingly, there remained a need to find an acceptable substitute for carbon tetrachloride, which would be useful to make chlorotrifluoroethylene polymer of controlled molecular weight, which, in turn, could then be combined with polychlorotrifluoroethylene oil to make a grease.